In the manufacture of aircraft, automotive and other complex mechanical assemblies, the situation often arises where screw fasteners such as bolts, nuts or screws must be torqued in a location which is restricted in access to conventional socket wrench sets, screwdrivers and hand operated box, open end or adjustable wrenches. In some cases, the factory installs a part and then hinders wrench access to the part by installing structure or other parts in the vicinity of the originally accessable part. Removal, adjustment or reinstallation of the reduced access part becomes a very difficult process and often requires disassembly of structure and/or machinery just to provide wrench access. In other cases, the aircraft, automobile or machine designer by error or oversight did not allow clearance for conventional wrench access to a part that requires maintenance or service. There are numerous special tools on the market that cater to the need for access to bolts, nuts and screws which are difficult to torque with conventional tools. The "Snap On" Tool Company, one of the largest suppliers of mechanics' tools, manufactures especially bent and shaped wrenches to fit deeply recessed parts such as distributors on cars as well as offset screwdrivers etc. all designed to ease the mechanic's job when servicing an automobile or airplane.
The need for an offset wrench has been demonstrated by the number of special wrenches available on the market and by the large number of companies that make and sell them. Almost every automobile parts supply store has racks of specialized wrenches and screwdrivers on display. Many of these are designed to fit a single model car or engine. There is a requirement and need for a general purpose offset wrench or screwdriver that the average mechanic could use on different tasks. The prior art has developed such offset torque application devices but they are either impractical or unsuitable for the average mechanic who requires a small device capable of providing torquing access in restricted quarters. The tool must be small enough to allow the mechanic to hold it with the same hand that applies the torque or to support it with a finger or two if required. U.S. Pat. No. 2,830,479 shows a design for a gear operated wrench which has an open frame supporting a gear train. This open framed device does provide means for applying torque to screw fasteners with restricted access but the open frame allows dirt and metal chips to enter the gear train and aggravate wear and breakage of the gear system. It also is a danger to the mechanic's hands because his skin could be pinched or abraded by the revolving gears as he grips the device with his hands or fingers to hold it in place. In addition, the open frame enclosing the gears is structurally deficient in that it has little restraint against torsion or bending because the frame comprises two long thin plates separated by spacers at the extremities. U.S. Pat. No. 3,987,691 shows an enclosed frame with a structurally more efficient housing that provides more rigidity but due to its greatly enlarged diameter at the driven and driving ends, the usefulness of the tool in close quarters is considerably reduced. U.S. Pat. No. 1,327,991 shows another version of an open framed wrench which has the structural limitations of the open frame and also the dangerous propensity of being capable of injuring the operator by trapping his hand between meshing gears or by abrading the operator's skin. None of these inventions has been a commercial success because they are too bulky, too limber, too dangerous to use and are susceptible to undue wear and breakage from dirt and debris.
All of the referenced patents support the gears by means of a central shaft which protrudes from each end of each gear and is supported by matching holes in the top and bottom of the housing as shown schematically in FIG. 1. This shaft or extension of the gear is really the fulcrum of a lever and sustains a load equal to twice the gear tooth force. The shaft and bearing combination are subject to wear due to the high unit loading. The lateral location of the gears depends not only on the precision with which the bearing holes are made in the housing but depend on the precision and manner in which the top and bottom of the housing are fastened together. Thus, in the case of a gear rotating about a separate shaft, there is the manufacturing tolerance (errors) between the concentricity of the bore of the gear with the pitch diameter of the gear as well as the location errors of the bearings for the shaft all added to the concentricity tolerances of the shaft and the looseness of the gear with respect to the shaft as well as the looseness between the shaft and bearings. Typically, this can add up to the order of 0.005-0.010 inches which cases uneven wear, stresses concentration on the gear teeth due to misalignment and also causes backlask to be designed into the system which in turn makes the wrench feel springy rather than firm to the operator.